1. Field of the Invention
The present invention relates to a wavelet transformation device and method, a wavelet inverse transformation device and method, a program, and a recording medium, and more particularly relates to a wavelet transformation device and method, a wavelet inverse transformation device and method, a program, and a recording medium, enabling high-speed wavelet transformation to be performed by exchanging data with internal memory.
2. Description of the Related Art
An image compression method representative of known methods is the JPEG (Joint Photographic Experts Group) method that has been standardized by the ISO (International Standards Organization). This is known to provide excellent coded images and decoded images in the event that DCT (Discrete Cosine Transform) is used and a relatively great number of bits are appropriated. However, reducing coding bits beyond a certain level results in marked block distortion characteristic of DCT, and deterioration can be subjectively observed.
On the other hand, in recent years, there has been much research performed on a method wherein images are divided into multiple bands (sub-bands) with filters called filter banks, wherein high-pass filters and low-pass filters are combined, and coding is performed for each band. Particularly, wavelet transformation coding is viewed as a new technology which is a likely candidate to replace DCT, since it does not have the problem that DCT has, i.e., marked block distortion at high compression rates.
International standardization of JPEG 2000 was completed January 2001. JPEG 2000 combines wavelet transformation and high-efficiency entropy coding (bit-plane based bit modeling and arithmetic encoding), and realizes marked improvements over JPEG with regard to coding efficiency.
Wavelet transformation uses a technique wherein, basically, image data is taken as input which is subjected to horizontal direction filtering and vertical direction filtering, in which lowband components are hierarchically divided. At this time, reading and writing of data to and from memory, such as readout of image data, writing of frequency coefficients generated as the result of filtering, readout of frequency coefficients once more, and so forth, need to be performed at a high frequency.
There has been recognized the need for a technique by which to perform wavelet transformation at high speeds, since image signals have a great amount of data. Also, a great number of techniques for externally writing frequency coefficients to memory and reading these in again have been proposed (See Japanese Unexamined Patent Application Publication No. 10-283342).